Body Composition and General Biochemical Background

Phosphorus is a vital element in the composition of all living matter and there is no known organism in which the chemistry of the element is not utilised. The human body contains many thousands of different phosphorus compounds, almost all of which are essential for its proper function. It contains very roughly 1% by weight of the element, about four fifths of this being present as hydroxyapatite in bones and teeth. Phosphorus constitutes about 0.3% of the total weight of the brain, about 0.2% 

The major elemental components of the human body are indicated in Table 11.2, and this is typical of animal species. The major components of plants lie in roughly the same sequence, the most notable difference being smaller quantities of calcium and phosphorus, due to the absence of large quantities of hydroxyapatite. Many other elements such as Na, Mg, Cu, Zn, V, Fe, Mn, Co, Cr, Mo, Se, F, Cl, I, Si, B and so forth, make up the remaining 0.5% in Table 11.2. 

Apart from the major involvement of N and P, there is as yet little evidence for any significant participation in human metabolism of the remaining pnictide elements As, Sb or Bi, whose concentrations in the body are normally 0.00003%. These elanents, and heavy metals such as Cd, Hg and Pb are normally regarded as toxic. 

Phosphorus is absorbed by animals from food (and by plants from the soil (Chapter 12.2)) in the form of phosphate ions HPO and H2PO4. In animals some of the element is found in this form in blood, urine and tissue fluids, but mostly as inorganic calcium salts in bones and teeth. The remaining phosphorus is present as organic phosphate , which is almost all in the form of numerous mono-and di-esters in which fully oxidised P is almost always linked indirectly to carbon through P-O-C bonds. In a few compounds P-NH-P linkages are formed. 

Some Important Phosphorus Compounds or Biopolymers, and Their Functions 

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